Optical communications networks are used to transport large amounts of voice and data through fiber optic cables. Wave-division multiplexing (WDM) can be used to transmit multiple channels of optical information through the same optical fiber. Multiple channels are carried in the same fiber by assigning different optical wavelengths to each channel. Data is communicated within a particular channel by pulses of optical energy using the wavelength assigned to that channel.
The optical signals degrade over distance such that re-generation or re-amplification may be required. Moreover, the channels within a fiber tend to degrade at different rates. Accordingly, determination and regulation of optical power on a channel-by-channel basis is desirable.
One technique used to enable optical power measurement on a channel-by-channel basis is to assign and introduce a sinusoidal pilot tone into each channel. Within a given fiber, each channel has a pilot tone distinct from the pilot tone of any other channel for the purpose of power calculations. The presence and power of a given channel is inferred by the presence of the pilot tone associated with that channel in the composite optical signal.
The spectral components contributed by the data for any channel may interfere with the pilot tone associated with a selected channel. For example, spectral peaks introduced by the framing pattern at multiples of the data frame rate can be mistaken for the pilot tone of the associated channel or any other channel. The data may have recurring patterns that introduce spectral components indistinguishable from the pilot tone. The spectral contributions from the data carried by any channel can create a false indication of the power or presence of the pilot tone of a selected channel.
Optical network management is compromised as a result of the false indications. Loss of a channel may not be detected as a result of a false positive. Detecting and locating faults within the optical network is made more complicated as a result of the false indications. Incorrect estimates of the channel power due to the spectral contributions of the data can result in improper amplification of a selected channel thus reducing the quality of the selected channel.